AC driven light emitting device

ABSTRACT

An alternating current (AC) driven light emitting device includes a substrate, K number of first light emitting diode (LED) cells arranged in a row on a top surface of the substrate, where K is an integer satisfying K≧3, K number of second LED cells arranged in a row parallel to the row of the first LED cells on the top surface of the substrate, and (K−1) number of third LED cells arranged in a row between the respective rows of the first and second LED cells on the top surface of the substrate. The AC driven light emitting device has a connection structure between LED cells to be operable at an AC.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Divisional of U.S. application Ser. No.12/265,357, filed on Nov. 5, 2008 now U.S. Pat. No. 8,040,050, whichclaims the priority of Korean Patent Application No. 2008-63127 filed onJun. 30, 2008, in the Korean Intellectual Property Office, thedisclosures of each of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an alternating current (AC) drivinglight emitting device, and more particularly, to an AC driven lightemitting device operable directly from AC power without requiring anAC-DC converter.

2. Description of the Related Art

A semiconductor light emitting diode (LED) is advantageous as a lightsource in terms of output, efficiency or reliability. Thus, thesemiconductor LED is actively studied and developed as a high-output,high-efficiency light source to substitute a backlight of anillumination device or a display device.

In general, the LED is driven at a low direct current (DC). Therefore,to be driven at a normal voltage of, e.g., AC 220V, the LED requires anadditional circuit such as an AC/DC converter for supplying a low DCoutput voltage. However, the additional circuit complicates theconfiguration of an LED module and may undermine efficiency andreliability when supply power is converted. Also, the additional partother than the light source increases costs and size of a product anddegrades electromagnetic interference (EMI) characteristic because of aperiodic component during an operation in a switching mode.

To overcome this limitation, various types of LED driving circuits,which can be driven directly at an AC voltage without using a converter,have been suggested. However, in a related art AC driven LED drivingcircuit, most LEDs are arranged to operate only in a specific half cycleof an AC voltage, thereby significantly increasing the number of LEDsneeded for obtaining the desired quantity of light.

The necessary number of LEDs may be varied according to arrangement ofthe LEDs even though identical quality of light is provided. However,the related art arrangement of LEDs has very low efficiency. Forexample, in a representative example where the LEDs are in areverse-parallel or bridge arrangement, the actual number of LEDscontinuously emitting light is merely 50% to 60% of the total number ofLEDs. That is, many LEDs are inefficiently used to attain a desiredlight-emission level.

Therefore, the LEDs need to be more efficiently arranged to provideequal quality of light through a smaller number of LEDs. The arrangementfor improved efficiency is significantly important in terms of costefficiency in manufacturing

selling the AC driven LED circuit.

In an actual AC driven light emitting device, unit LED cells may beconnected with one another with great complexity. Thus, theinterconnections and processes for forming them may be complicated andless productive. Because of the complicated interconnections between theplurality of LED cells, it is also important to design a light emittingdevice to be miniaturized with a high degree of integration.

SUMMARY OF THE INVENTION

An aspect of the present invention provides an excellent AC driven lightemitting device, which has a connection structure allowing operation atan AC voltage while optimizing interconnection and arrangement of LEDcells for a high degree of integration.

According to an aspect of the present invention, there is provided analternating current (AC) driven light emitting device including: asubstrate; K number of first light emitting diode (LED) cells arrangedin a row on a top surface of the substrate, where K is an integersatisfying K≧3; K number of second LED cells arranged in a row parallelto the row of the first LED cells on the top surface of the substrate;and (K−1) number of third LED cells arranged in a row between therespective rows of the first and second LED cells on the top surface ofthe substrate.

The AC driven light emitting device has a connection structure betweenthe LED cells to be operable at an AC.

A first electrode of the m^(th) third LED cell is connected with secondelectrodes of the m^(th) and m+1^(th) first LED cells, and a secondelectrode of the m^(th) third LED cell is connected with firstelectrodes of the m^(th) and m+1^(th) second LED cells, where m is anodd number satisfying m<K.

A first electrode of the n^(th) third LED cell is connected with secondelectrodes of the n^(th) and n+1^(th) second LED cells, and a secondelectrode of the nth third LED cell is connected with first electrodesof the n^(th) and n+1^(th) first LED cells, where n is an even numbersatisfying n<K.

The AC driven light emitting device further includes: a first externalelectrode connected with a first electrode of the first first LED celland a second electrode of the first second light LED cell; and a secondexternal electrode connected with electrodes among electrodes of theK^(th) first and second LED cells, which are not in connection with thethird LED cell.

First and second electrodes of each of the first to third LED cells maybe respectively disposed adjacent to both facing sides on a top surfaceof a corresponding one of the first to third LED cells, and each mayhave a portion extending along the corresponding side thereof. Thus, theuniform current distribution is achieved over the entire light emissionarea of each LED cell, thereby improving the high light emissionefficiency.

The substrate may have a top surface having a rectangular shape withfirst to fourth sides. In this case, the first and second LED cells maybe respectively arranged in rows along the first and second sides, thefirst first and second LED cells may be disposed adjacent to the thirdside, and the K^(th) first and second LED cells may be disposed adjacentto the fourth side.

To realize the high degree of integration, the third LED cell isarranged adjacent to two first LED cells having connected electrodestherebetween, and two second LED cells having connected electrodestherebetween.

The third LED cell may have a top surface with a parallelogram shapeinclined with respect to an arrangement direction thereof.

In order to shorten the electrode interconnection and thus reducedefects, the first and second electrodes of the third LED cell may berespectively disposed adjacent to both inclined sides on the top surfaceof the third LED cell.

In this case, the first and second electrodes of the first LED cell maybe respectively disposed adjacent to both sides on the top surface ofthe first LED cell, which are perpendicular to an arrangement directionof the first LED cells, and the first and second electrodes of thesecond LED cell may be respectively disposed adjacent to both sides onthe top surface of the second LED cell, which are perpendicular to anarrangement direction of the second LED cells.

The third LED cell may have a top surface having a rough rectangularshape with two facing longer sides and two facing shorter sides.

The first and second electrodes of the third LED cell may berespectively disposed adjacent to the two longer sides of the topsurface having the rectangular shape.

The third LED cell may be arranged such that the longer side thereof isalmost perpendicular to an arrangement direction of the third LED cells.The first and second electrodes of the first LED cell may berespectively disposed adjacent to both sides on the top surface of thefirst LED cell, which are parallel to the arrangement direction of thefirst LED cells. The first and second electrodes of the second LED cellmay be disposed adjacent to both sides on the top surface of the secondLED cell, which are parallel to the arrangement direction of the secondLED cells.

To connect the first and second LED cells with external electrodes witha high degree of integration, the first first LED cell may extend alongthe third side of the top surface of the substrate to be adjacent to thefirst second LED cell, and the K^(th) second LED cell may extend alongthe fourth side of the top surface of the substrate to be adjacent tothe K^(th) first LED cell.

In this case, the first external electrode may be placed on the firstfirst LED cell, and the second external electrode may be placed on theK^(th) second LED cell.

To prevent voltage concentration at a specific cell, the first to thirdLED cells may have almost the same light emission areas.

The first to third LED cells each may be obtained from a firstconductivity type semiconductor layer, an active layer and a secondconductivity type semiconductor layer which are sequentially grown onthe substrate. That is, desired arrangements of the first to third LEDcells may be obtained by isolating the first conductivity semiconductorlayer, the active layer and the second conductivity type semiconductorlayer, which are grown on the entire top surface of the substrate for alight emission structure, in units of cells using an appropriateisolation process.

The isolation process may be categorized into a full-isolation processfor exposure up to a substrate or a half-isolation process of exposureonly up to the first conductivity type semiconductor layer.

For example, at least one pair of the m^(th) and m+1^(th) second LEDcells may be isolated from each other by an exposed region of the firstconductivity type semiconductor layer, and share one first electrodedisposed in the exposed region of the first conductivity typesemiconductor layer.

Similarly, at least one pair of the n^(th) and n+1^(th) first LED cellsmay be isolated from each other by an exposed region of the firstconductivity type semiconductor layer, and share one first electrodedisposed in the exposed region of the first conductivity typesemiconductor layer.

As the half-isolation process is applied to a specific cell and thefirst electrode is shared, a process can be simplified and the degree ofintegration can be improved.

Every pair of the m^(th) and m+1^(th) second LED cells may be isolatedfrom each other by an exposed region of the first conductivity typesemiconductor layer, and share one first electrode disposed in theexposed region of the first conductivity type semiconductor layer. Everypair of the n^(th) and n+1^(th) first LED cells may be isolated fromeach other by an exposed region of the first conductivity typesemiconductor layer, and share one first electrode disposed in theexposed region of the first conductivity type semiconductor layer. Otherremaining first to third LED cells may be isolated by exposed regions ofthe substrate.

All the first to third LED cells may be isolated from another adjacentLED cell by an exposed region of the substrate (i.e., by thefull-isolation process).

According to another aspect of the present invention, there is providedan alternating current (AC) driving light emitting device including: asubstrate; and first and second ladder network circuit type LED arraysdisposed parallel to each other on a top surface of the substrate. Eachof the first and second ladder network circuit type LED arrays includes:K number of first LED cells arranged in a row on the top surface of thesubstrate, where K is an integer satisfying K≧3; K number of second LEDcells arranged in a row parallel to the row of the first LED cells onthe top surface of the substrate; and (K−1) number of third LED cellsarranged in a row between the respective rows of the first and secondLED cells on the top surface of the substrate.

The first and second ladder network circuit type LED arrays are arrangedsuch that the respective rows of the second LED cells of the first andsecond ladder network circuit type LED arrays are adjacent to eachother.

A first electrode of the m^(th) third LED cell is connected with secondelectrodes of the m^(th) and m+1^(th) first LED cells, and a secondelectrode of the m^(th) third LED cell is connected with firstelectrodes of the m^(th) and m+1^(th) second LED cells, where m is aninteger satisfying m<K. A first electrode of the n^(th) third LED cellis connected with second electrodes of the n^(th) and n+1^(th) secondLED cells, and a second electrode of the n^(th) third LED cell isconnected with first electrodes of the n^(th) and n+1^(th) first LEDcells.

A first electrode of the first first LED cell and a second electrode ofthe first second LED cell are connected together, and electrodes of theK^(th) first and second LED cells, which are not in connection with thethird LED cell, are connected together.

For the connection between the first and second ladder network circuittype LED arrays, electrodes of the K^(th) second LED cell of the firstladder network circuit type LED array and the K^(th) second LED cell ofthe second ladder network circuit type LED array, which are not inconnection with the third LED cell, are connected together.

Each of the first to third LED cells of each of the first and secondladder network circuit type LED arrays may include a first conductivitytype semiconductor layer, an active layer and a second conductivity typesemiconductor layer sequentially grown on the substrate.

When the K representing the number of the first LED cells and the numberof second LED cells in each of the first and second ladder networkcircuit type LED arrays is an odd number, the K^(th) second LED cell ofthe first ladder network circuit type LED array and the K^(th) secondLED cell of the second ladder network may be isolated from each other byan exposed region of the first conductivity type semiconductor layer,and share one first electrode.

Also, a third ladder network circuit type LED array having a similarconfiguration as described above may be connected thereto.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other aspects, features and other advantages of thepresent invention will be more clearly understood from the followingdetailed description taken in conjunction with the accompanyingdrawings, in which:

FIG. 1A illustrates a light emitting diode (LED) driving circuitaccording to an exemplary embodiment (unit arrangement) of the presentinvention;

FIG. 1B illustrates arrangement of LED cells for implementation of alight emitting device based on the LED driving circuit of FIG. 1A;

FIG. 2 is a plan view of a light emitting device according to anexemplary embodiment of the present invention;

FIGS. 3A through 3D are side sectional views of the light emittingdevice of FIG. 2;

FIG. 4 is a plan view of a light emitting device according to anotherexemplary embodiment of the present invention;

FIG. 5 is a plan view of a light emitting device according to apreferred exemplary embodiment of the present invention;

FIG. 6 is an equivalent circuit diagram of the light emitting device ofFIG. 5; and

FIGS. 7A through 7C are a plan view and side sectional views of aconnection portion of ladder network circuit rows of the light emittingdevice of FIG. 6.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Exemplary embodiments of the present invention will now be described indetail with reference to the accompanying drawings.

FIG. 1A is a light emitting diode (LED) driving circuit according to anexemplary embodiment (unit arrangement) of the present invention.

The LED driving circuit of FIG. 1A includes three first LED cells A1, A2and A3, three second LED cells B1, B2 and B3, and two third LED cells C1and C2. The three first LED cells A1, A2 and A3, and the three secondLED cells B1, B2 and B3 are connected in parallel to one another betweenfirst and second contacts provided as external terminals P1 and P2. Thetwo third LED cells C1 and C2 are respectively connected between ajunction point between the first LED cells A1 and A2 and a junctionpoint between the second LED cells B1 and B2 and between a junctionpoint between the first LED cells A2 and A3 and a junction point betweenthe second LED cells B2 and B3.

Electrode connections of the first to third LED cells will now bedescribed. The first third LED cell C1 has a first electrode (−)connected with respective second electrodes (+) of the first and secondfirst LED cells A1 and A2, and a second electrode (+) connected withrespective first electrodes (−) of the first and second second LED cellsB1 and B2. The second third LED cell C2 has a first electrode (−)connected with respective second electrodes (+) of the second and thirdsecond LED cells B2 and B3, and a second electrode (+) connected withrespective first electrodes (−) of the second and third first LED cellsA2 and A3.

The first contact is connected with a first electrode (−) of the firstfirst LED cell A1 and a second electrode (+) of the first second LEDcell B1. The second contact is connected with a second electrode (+) ofthe third first LED cell A3 and a first electrode of the third secondLED cell B3.

The connection structure described above allows the LED driving circuitof FIG. 1A to be driven in different half cycles of an alternatingcurrent (AC).

In a first half cycle of the AC current, a group of LED cellsB1-C1-A2-C2-B3 connected together in series forms a first current loop.In a second half cycle of the AC voltage, a group of LED cellsA3-C2-B2-C1-A1 connected together in series forms a second current loop.Through this operation, the two third LED cells C1 and C2 can becontinuously driven over the entire cycle of the AC voltage.

In an actual ladder network circuit, five LED devices may be provided toperform continuous emission. Here, a ratio of the number of driven LEDsto the number of employed LEDs is 62.5% (⅝=62.50), which is higher thanin the case of the related art AC-driven LED arrangement, for example, areverse-polarity arrangement (50%) or a bridge arrangement (generally60%).

The present invention provides a layout for implementing a laddernetwork LED driving circuit as exemplified in FIG. 1A. The layout of LEDcells can ensure the high degree of integration and excellent lightemission efficiency and simplify the connection between electrodes.

FIG. 1B is a schematic view of one example of the present invention,illustrating a schematic layout of LED cells for implementing thecircuit of FIG. 1A as a light emitting device.

Referring to FIG. 1B, three first LED cells A1, A2 and A3 a are arrangedin a row, and three second LED cells B1, B2 and B3 are arranged in a rowparallel to the first LED cells A1, A2 and A3. Two third LED cells C1and C2 are arranged between the row of the first LED cells A1, A2 and A3and the row of the second LED cells B1, B2 and B3.

The above arrangement in which the third LED cells C1 and C2 aredisposed between the first and second LED cells contribute to achievinga simple implementation of lines ac1, ac2, bc1 and bc2.

As shown in FIG. 1B, the AC driven light emitting device according tothe present invention includes lines ac1, bc1, ac2 and bc2. The line ac1connects the first electrode (−) of the first third LED cell C1 with therespective second electrodes (+) of the first and second first LED cellsA1 and A2. The line bc1 connects the second electrode (+) of the firstthird LED cell C1 with the respective first electrodes (−) of the firstand second second LED cells B1 and B2. The line ac2 connects the secondelectrode (+) of the second third LED cell C2 with the respective firstelectrodes (−) of the second and third first LED cells A2 and A3. Theline bc2 connects the first electrode (−) of the second third LED cellC2 with the respective second electrodes (+) of the second and thirdsecond LED cells B2 and B3. The lines between the cells may beconfigured using known lines such as air-bridges, wires or the like.

Also, the first contact P1 is connected with the first electrode (−) ofthe first first LED cell A1 and the second electrode (+) of first secondLED cell B1. The second contact P2 is connected with the secondelectrode (+) of the third first LED cell A3 and the first electrode (−)of the third second LED cell B3.

FIG. 2 is a plan view of a light emitting device according to anexemplary embodiment of the present invention. FIG. 2 may be understoodas illustrating a desirable light emitting device, which is an actualimplementation of FIG. 1B.

The AC driven light emitting device of FIG. 2 includes a substrate 31having a rectangular shape with four sides, i.e., first to fourth sidese1 to e4.

Three first LED cells A1, A2 and A3 are arranged in a row along thefirst side e1 of a top surface of the substrate 31. Three second LEDcells B1, B2 and B3 are arranged in a row along the second side e2facing the first side e1. Two third LED cells C1 and C2 are arrangedbetween the respective rows of the first LED cells A1, A2 and A3 and thesecond LED cells B1, B2 and B3.

As for the first to third LED cells employed in this embodiment, a firstelectrode 37 or 37′ and a second electrode 38 are respectively disposedadjacent to facing sides of a top surface of a corresponding one of theLED cells. The first and second electrodes 37, 37′ and 38 each have aportion extending along the corresponding side adjacent thereto. Sincethe first electrodes 37 or 37′ and the electrodes 38 respectively extendalong both opposing sides, uniform current distribution can be obtainedover the entire emission area of each LED cell. This can improve lightemission efficiency.

According to this embodiment, the first first LED cell A1 may extend upto the first second LED cell B1 along the third side e3 of the topsurface of the substrate 31. The third second LED cell B3 may extend upto the third first LED cell A3 along the fourth side e4 of the topsurface of the substrate 31. The higher degree of integration can beachieved by adjusting the sizes and shapes of the LED cells.

The AC driven light emitting device includes a first external electrodeP1 and a second external electrode P2. The first external electrode P1is connected with a first electrode of the first first LED cell A1 and asecond electrode of the first second LED cell B1. The second externalelectrode P2 is connected with a second electrode of the third first LEDcell A3 and a first electrode of the third second LED cell B3.

As shown in FIG. 2, the first external electrode P1 may be placed on thefirst first LED cell A1, and the second external electrode P2 may beplaced on the third second LED cell B3. Compared to other LED cells, theextending LED cells A1 and B3 are more advantageous by having greaterlight-emitting areas. Therefore, areas for the first and second externalelectrodes P1 and P2 can be easily ensured in the extending LED cells A1and B3, respectively. The first to third LED cells may have almost thesame light-emission area to prevent concentration of current on aspecific cell.

The term “light-emission area” used in this application means an areaparticipating in light emission, and may be understood as an area of anactive layer of each cell.

FIGS. 3A through 3D are side sectional views of the light emittingdevice of FIG. 2.

The first to third LED cells of the AC driven light emitting deviceaccording to this embodiment may be obtained from a first conductivitytype semiconductor layer 34, an active layer 35, and a secondconductivity type semiconductor layer 36 sequentially grown on thesubstrate 31. That is, the first conductivity type semiconductor layer34, the active layer 35 and the second conductivity type semiconductorlayer 36 are grown on the entire top surface of the substrate 31 for alight emitting structure. Thereafter, a resulting structure is isolatedin units of cells, using a proper isolation process, thereby obtainingthe arrangement of a plurality of first to third LED cells illustratedin FIG. 1.

FIGS. 3A through 3D are side sectional views of the light emittingdevice of FIG. 2, illustrating isolation of each cell unit, which may bepreferably employed. The structure illustrated in FIG. 2 will now bedescribed in more detail with reference to FIGS. 3A through 3D.

FIG. 3A is a cross-sectional view taken along line X1-X1′ of the lightemitting device of FIG. 2.

Referring to FIG. 3A, the first first LED cell A1 and the second firstLED cell A2 are isolated from each other by a full-isolation process I1for exposing a substrate region, whereas the second first LED cell A2and the third first LED cell A3 may be separated by a half-isolationprocess 12 for exposing a region of the first conductivity typesemiconductor layer 34. The second first LED cell A2 and the third firstLED cell A3 may share the first electrode 37′ disposed in the exposedregion of the first conductivity type semiconductor layer 34.

The half-isolation process is partially performed within a rangeallowing the implementation of a desired driving circuit, and the firstelectrode 37′ is disposed in the exposed region of the firstconductivity type semiconductor layer 34. In such a manner, an electrodeshared by adjacent cells is provided, so that the process can besimplified and the degree of integration can be improved.

FIG. 3B is a cross-sectional view taken along line X2-X2′ of the lightemitting device of FIG. 2.

As shown in FIG. 3B, the first first LED cell A1 and the third secondLED cell B3 are isolated from the third LED cells C1 and C2 by thefull-isolation process I1, and the second LED cells B1 and B2 areisolated from each other by the full-isolation process I1.

FIG. 3C is a cross-sectional view taken along line Y1-Y1′ of the lightemitting device of FIG. 2.

As shown in FIG. 3C, the first LED cell A2, the second LED cell B1 andthe third LED cell C1 are isolated from each other by the full-isolationprocess I1. Lines 39 between electrodes of the cells may be configuredby air bridges or wires as described above.

FIG. 3D is a cross-sectional view taken along line Y2-Y2′ of the lightemitting device of FIG. 2.

As shown in FIG. 3D, the first first LED cell A1 and the first secondLED cell B1 are isolated from each other by the full-isolation processI1. The isolation and connection of the third first and second LED cellsA2 and B3 may be understood in the similar manner.

Of course, unlike this embodiment, all the first to third LED cells maybe isolated from other adjacent LED cells by exposing regions of thesubstrate 31, i.e., by the full-isolation process. Each cell may haveindividual first and second electrodes without sharing them.

As shown in FIG. 2, the third LED cell C1/C2 may be arranged adjacent tothe two first LED cells A1 and A2/A2 and A3 having connected electrodesand the two second LED cells B1 and B2/B2 and B3 having connectedelectrodes. This can increase the degree of integration and shortenlines used for the electrode connection between the LED cells.

As shown in FIG. 2, each of the third LED cells C1 and C2 may have a topsurface with a parallelogram shape inclined with respect to anarrangement direction thereof. The first and second electrodes 37 and 38of each of the third LED cells C1 and C2 may be disposed adjacent toboth inclined sides on a top surface of a corresponding one of the thirdLED cells C1 and C2. This design of the third LED cells C1 and C2 cancontribute to further shortening the lines used for the electrodeconnection and thus reducing defects that may be caused during a lineformation process and unfavorable shadow effect of long non-transparentline on emission efficiency.

To simplify the line connections, the first and second electrodes 37 and38 of each of the first LED cells A1, A2 and A3 may be disposed adjacentto both sides on a top surface of a corresponding one of the first LEDcells A1, A2 and A3, which are perpendicular to the arrangementdirection of the corresponding first LED cell. The first and secondelectrodes 37 and 38 of each of the second LED cells B1, B2 and B3 maybe disposed adjacent to both sides on a top surface of a correspondingone of the second LED cells B1, B2 and B3, which are perpendicular tothe arrangement direction of the corresponding second LED cell.

Such arrangement may be variously implemented. For example, arrangementmay be made as illustrated in FIG. 4 without being limited to the oneillustrated in FIG. 2.

Similarly to the previous embodiment, a light emitting device of FIG. 4may have a structure obtained by sequentially forming a firstconductivity type semiconductor layer 44, an active layer (not shown)and a second conductivity type semiconductor layer 46 on a substrate,and then isolating a resulting structure in proper units of cells. Thestructure obtained by the cell-unit isolation process may be understoodas a structure similar to that described with reference to FIGS. 3Athrough 3D.

According to this embodiment, the third LED cells C1 and C2 each have atop surface having a rough rectangular shape with two longer sides andtwo shorter sides. Of course, this infers that each of the third LEDcells C1 and C2 may also have an exact rectangular shape, not just thepartially transformed rough rectangular shape, for a higher degree ofintegration.

According to this embodiment, the first and second electrodes 47 and 48of each of the third LED cells C1 and C2 may be disposed adjacent to twolonger sides of the rectangular top surface thereof.

In this case, the third LED cells C1 and C2 may be arranged such thattheir longer sides become roughly perpendicular to the arrangementdirection of the third LED cells C1 and C2.

First and second electrodes 47 and 48 of each of the first LED cells A1to A3 may be respectively disposed adjacent to both sides of a topsurface of a corresponding one of the first LED cell A1 to A3, which areparallel to the arrangement direction of the first LED cells A1 to A3.The first and second electrodes 47 and 48 of each of the second LEDcells B1 to B3 may be respectively disposed adjacent to both sides of atop surface of a corresponding one of the second LED cells B1 to B3,which are parallel to the arrangement direction of the second LED cellsB1 to B3.

A light emitting device including three first LED cells, three secondLED cells and two third LED cells has been described for the betterunderstanding of the present invention. However, the present inventionis not limited thereto and may be similarly applied to embodiments withmore LED cells.

The present invention may be expressed as follows when the number ofspecific cells is not defined but generalized.

According to the present invention, an AC driven light emitting deviceincludes K number of first LED cells, K number of second LED cells, and(K−1) number of third LED cells. Here, K is an integer satisfying K≧3.The first LED cells are arranged in a row, and the second LED cells arealso arranged in a row. The third LED cells are disposed between therows of the first and second LED cells. In this case, electrodeconnections between the first to third LED cells may be expressed asfollows.

In the following description, respective sequences of the first to thirdLED cells are described as being arranged in one arrangement direction.The m^(th) third LED cell has a first electrode connected with secondelectrodes of the m^(th) and m+1^(t)h first LED cells, and a secondelectrode connected with first electrodes of the m^(th) and m+1^(th)second LED cells. Here, m is an odd number satisfying m<K. The n^(th)third LED cell has a first electrode connected with second electrodes ofthe n^(th) and n+i^(th) second LED cells, and a second electrodeconnected with first electrodes of the n^(th) and n+1^(th) first LEDcells. Here, n is an even number satisfying n<K.

A first electrode of the first first LED cell and a second electrode ofthe first second LED cell are connected together to form a contact to beprovided as a first external electrode. Electrodes of the last K^(th)first and second LED cells, which are not in connection with the thirdLED cell, are connected together to form a contact to be provided as asecond external electrode.

The isolation described with reference to FIGS. 3A through 3D may begeneralized as follows.

Every pair of the m^(th) and m+1^(th) second LED cells may be designedto be isolated from each other by an exposed region of a firstconductivity type semiconductor layer and to share one first electrodedisposed in the exposed region of the first conductivity typesemiconductor layer. Similarly, every pair of the n^(th) and n+1^(th)first LED cells may be designed to be isolated by an exposed region ofthe first conductivity type semiconductor layer and to share one firstelectrode disposed in an exposed region of the first conductivity typesemiconductor layer.

In this case, the remaining adjacent first to third LED cells may beisolated by the full-isolation process of exposing a region of asubstrate.

FIG. 5 is a plan view of a light emitting device according to anexemplary embodiment of the present invention, and FIG. 6 is anequivalent circuit diagram of the light emitting device of FIG. 5.

A light emitting device 100 of FIG. 5 includes a substrate 101, andfirst to third ladder network circuit type LED arrays 110, 120 and 130disposed parallel to one another on the substrate 101. LED cells of eachof the first to third ladder network circuit type LED arrays 110, 120and 130 are arranged from one side toward an opposing side (see dottedlines in FIG. 5).

The first ladder network circuit type LED array 110 includes thirteenfirst LED cells 110A, thirteen second LED cells 110B, and twelve thirdLED cells 110C. The first LED cells 110A are arranged in a row on a topsurface of the substrate 101, and the second LED cells 110B are alsoarranged in a row on the top surface of the substrate 101. The third LEDcells 110C are arranged in a row between the rows of the first andsecond LED cells 110A and 110B to be parallel thereto. The second laddernetwork circuit type LED array 120 includes thirteen first LED cells120A, thirteen second LED cells 120B, and twelve third LED cells 120C.The first LED cells 120A are arranged in a row on a top surface of thesubstrate 101, and the second LED cells 120B are also arranged in a rowon the top surface of the substrate 101. The third LED cells 120C arearranged in a row between the rows of the first and second LED cells120A and 120B to be parallel thereto. The third ladder network circuittype LED array 130 includes thirteen first LED cells 130A, thirteensecond LED cells 130B, and twelve third LED cells 130C. The first LEDcells 130A are arranged in a row on a top surface of the substrate 101,and the second LED cells 130B are also arranged in a row on the topsurface of the substrate 101. The third LED cells 130C are arranged in arow between the rows of the first and second LED cells 130A and 130B tobe parallel thereto.

Each of the first to third ladder network circuit type LED arrays 110 to130 has a connection structure between first to third LED cells forimplementing a ladder network circuit. This connection structure may beimplemented in a similar manner to that of the connection structurebetween the LED cells illustrated in FIG. 2.

For ease of the description of the connection between LED cells employedin this embodiment, respective sequences of the first to third LED cellsare defined in one arrangement direction (here, in a direction from theright toward the left).

A first electrode 117 of the m^(th) third LED cell 110C is connectedwith second electrodes 118 of the m^(th) and m+1^(th) first LED cells110A. Here, m is an odd number satisfying m<13. A second electrode 118of the m^(th) third LED cell 110C is connected with first electrodes 117of the m^(th) and m+1^(th) second LED cells 110B. This electrodeconnection is employed to the first to third ladder network circuit typeLED arrays 110, 120 and 130 in the same manner.

A first electrode 117 of the n^(th) third LED cell 110C is connectedwith second electrodes 118 of the n^(th) and n+1^(th) second LED cells110B. Here, n is an even number satisfying n<13. A second electrode 118of the n^(th) third LED cell 110C is connected with first electrodes 117of the n^(th) and n+1^(th) first LED cells 110A. This electrodeconnection is employed to the first to third ladder network circuit typeLED arrays 110, 120 and 130 in the same manner.

A first electrode of the first first LED cell and a second electrode ofthe first second LED cell are connected with each other. Electrodes ofthe last first and second LED cells, which are not in connection withthe third LED cell, are connected with each other. That is, a secondelectrode of the 13^(th) first LED cell and a first electrode of the13^(th) second LED cell are connected with each other.

The above connections between the electrodes of the LED cells may beimplemented by interconnection units 119, 129 and 139. For example, aknown interconnection unit such as an air bridge or a wire may be used,but the present invention is not limited thereto.

As described so far, the details described with reference to FIGS. 2 and3A through 3D may be incorporated with this embodiment if they do notdepart from the teaching of this embodiment.

For example, the first to third LED cells each may be a structureobtained by separating a stack of a first conductivity typesemiconductor layer 104, an active layer 105 and a second conductivitytype semiconductor layer 106 sequentially grown on a substrate 101 usingan appropriate isolation process (see FIGS. 7A through 7C). Also, thefirst and second LED cells may be isolated by the exposure only up tothe first conductivity type semiconductor layer so that the firstelectrode may be shared in units of two adjacent cells (see FIG. 3A).

As shown in the drawings, the third LED cells 110C, 120C and 130C eachmay have a top surface having a parallelogram inclined with respect toits arrangement direction. In the third LED cells 110C, 120C and 130C,the first electrode 117, 127 or 137 and the second electrode 118, 128 or138 may be respectively disposed adjacent to both inclined sides on atop surface of a corresponding one of the third LED cells 110C, 120C and130C. The design of the third LED cells 110C, 120C and 130C may shortenthe electrode interconnections.

Furthermore, to implement simpler interconnections, in the first LEDcells 110A, 120A and 130A, the first electrode 117, 127 or 137 and thesecond electrode 118, 128 or 138 may be respectively disposed adjacentto both sides of a top surface of a corresponding one of the first LEDcells 110A, 120A and 130A, which are perpendicular to the arrangementdirection of the corresponding first LED cell. In the second LED cells110C, 120C and 130C, the first electrode 117, 127 or 137 and the secondelectrode 118, 128 or 138 may be respectively disposed adjacent to bothsides of a top surface of a corresponding one of the second LED cells110C, 120C and 130C, which are perpendicular to an arrangement directionof the corresponding second LED cell.

According to this embodiment, the second ladder network circuit type LEDarray 120 is arranged to be placed between the first and second laddernetwork LED arrays 110 and 130.

The first and second ladder network circuit type LED arrays 110 and 120are arranged such that the respective rows of the second LED cells 110Band 120B of the first and second ladder network circuit type LED arrays110 and 120 are placed adjacent to each other. The second and thirdladder network circuit type LED arrays 120 and 130 are arranged suchthat the respective rows of the first LED cells 120A and 130A thereofare placed adjacent to each other.

Through this arrangement, a connection between the ladder networkcircuits described below can be easily implemented. According to thisembodiment, the second ladder network circuit type LED array 120 iselectrically connected with adjacent first and third ladder networkcircuit type LED arrays 110 and 130 at both ends.

FIGS. 7A through 7C are a plan view and side sectional viewsillustrating a connection portion A of the light emitting device of FIG.5.

An electrode of the 13^(th) second LED cell 110B of the first laddernetwork circuit type LED array 110, which is not in connection with thethird LED cell 110C (i.e., the first electrode 117 in this embodiment)is connected with an electrode of the 13^(th) second LED cell 120B ofthe second ladder network circuit type LED array 120, which is not inconnection with the third LED cell 120C (i.e., the first electrode 127in this embodiment).

Similarly, an electrode of the first first LED cell 120A of the secondladder network circuit type LED array 120, which is not in connectionwith the third LED cell 110C (i.e., the first electrode 127 in thisembodiment) is connected with an electrode of the 13^(th) first LED cell130A of the second ladder network circuit type LED array 130, which isnot in connection with the third LED cell 130C (i.e., the firstelectrode 137 of this embodiment).

According to this embodiment, a connection electrode between laddernetwork circuits is implemented in the form of a common electrode,thereby facilitating the connection between the ladder network circuits.

As shown in FIGS. 7A through 7C, the thirteenth second LED cell 110B ofthe first ladder network circuit type LED array 110 and the thirteenthsecond LED cell 120B of the second ladder network circuit type LED array120 may be obtained using a half isolating process of exposing a regionof the first conductivity type semiconductor layer 104 in a T shape whenviewed from the top. A first common electrode 107 is disposed at aportion adjacent to one-side region of a substrate in the exposedregion, so that two LED cells can share the first common electrode 107and the aforementioned connection between the ladder network circuitscan be realized.

Similarly, the first second LED cell 120B of the second ladder networkcircuit type LED array 120 and the first second LED cell 130B of thethird ladder network circuit type LED array 130 may be obtained using ahalf-isolation process of exposing a region of the first conductivitytype semiconductor layer 104 in a T shape when viewed from the top. Afirst common electrode 107 is disposed at a portion adjacent to one-sideregion of a substrate in the exposed region, so that two LED cells canshare the first common electrode 107 and the aforementioned connectionbetween the ladder network circuits can be realized.

Thus, the first through third ladder network circuits 110, 120 and 130,like an equivalent circuit illustrated in FIG. 6, are electricallyconnected in series to one another to implement an AC driven lightemitting device having a configuration of a desired ladder networkcircuit.

According to this embodiment, the light emitting device with threeladder network circuit type LED arrays has been described. However, thepresent invention is not limited by the number of ladder network circuittype LED arrays. For example, a light emitting device may include justtwo ladder network circuit type LED arrays or four or more laddernetwork circuit type LED arrays. Of course, it is obvious to thoseskilled in the art that the number of LED cells belonging to each laddernetwork circuit type LED array is not limited to those illustrated inthe accompanying drawings.

According to the present invention, an AC driven light emitting deviceis provided, which has an optimized ladder network circuit typeconnection structure for an operation at an AC to attain a high degreeof integration. Particularly, AC driven light emitting devices of highproductivity can be provided by arranging LED cells and placing andconnecting electrodes so as to simplify the connection between the LEDcells while ensuring high efficiency of each LED cell.

While the present invention has been shown and described in connectionwith the exemplary embodiments, it will be apparent to those skilled inthe art that modifications and variations can be made without departingfrom the spirit and scope of the invention as defined by the appendedclaims.

1. An alternating current (AC) driven light emitting device comprising:a substrate; K number of first LED cells arranged in a row on a topsurface of the substrate, where K is an integer satisfying K≧3; K numberof second LED cells arranged in a row parallel to the row of the firstLED cells on the top surface of the substrate; (K−1) number of third LEDcells arranged in a row between the respective rows of the first andsecond LED cells on the top surface of the substrate, a first externalelectrode connected with a first electrode of a first one of the firstLED cells and a second electrode of a first one of the second LED cells;and a second external electrode connected with electrodes amongelectrodes of the K^(th) first and second LED cells, which are not inconnection with the third LED cell wherein the AC driven light emittingdevice has first and second current loops each driven in each a halfcycle of an alternating voltage applied between the first and secondexternal electrodes, wherein the first current loop has (2r−1) sequenceof the first LED cells, 2r sequence of the second LED cells and the(K−1) number of third LED cells, respectively to be connected in series;and the second current loop has 2r sequence of the first LED cells,(2r−1) sequence of the second LED cells and the (K−1) number of thirdLED cells, respectively to be connected in series, where r is a positiveinteger defining sequences of the respective first to third LED cellswith respect to the first external electrode.
 2. The AC driven lightemitting device of claim 1, wherein a first electrode of the (2r−1)^(th)third LED cell is connected with second electrodes of the (2r−1)^(th)and 2r^(th) first LED cells, and a second electrode of the (2r−1)^(th)third LED cell is connected with first electrodes of the (2r−1)^(th) and2r^(th) second LED cells, a first electrode of the 2r^(th) third LEDcell is connected with second electrodes of the 2r^(th) and 2r+1^(th)second LED cells, and a second electrode of the 2r^(th) third LED cellis connected with first electrodes of the 2r^(th) and 2r+1^(th) firstLED cells.
 3. The AC driven light emitting device of claim 2, whereinfirst and second electrodes of each of the first to third LED cells arerespectively disposed adjacent to both facing sides on a top surface ofa corresponding one of the first to third LED cells, and each have aportion extending along the corresponding side thereof.
 4. The AC drivenlight emitting device of claim 3, wherein the substrate has a topsurface having a rectangular shape with first to fourth sides, and thefirst and second LED cells are respectively arranged in rows along thefirst and second sides, the first ones of the first and second LED cellsare disposed adjacent to the third side, and the K^(th) first and secondLED cells are disposed adjacent to the fourth side.
 5. The AC drivenlight emitting device of claim 4, wherein the first and second sideseach have a longer length than the third and fourth sides.
 6. The ACdriven light emitting device of claim 5, wherein the third LED cell isarranged adjacent to two first LED cells having connected electrodestherebetween, and two second LED cells having connected electrodestherebetween.
 7. The AC driven light emitting device of claim 6, whereinthe third LED cell has a top surface with a parallelogram shape inclinedwith respect to an arrangement direction thereof.
 8. The AC driven lightemitting device of claim 7, wherein the first and second electrodes ofthe third LED cell are respectively disposed adjacent to both inclinedsides on the top surface of the third LED cell.
 9. The AC driven lightemitting device of claim 8, wherein the first and second electrodes ofthe first LED cell are respectively disposed adjacent to both sides onthe top surface of the first LED cell, which are perpendicular to anarrangement direction of the first LED cells, and the first and secondelectrodes of the second LED cell are respectively disposed adjacent toboth sides on the top surface of the second LED cell, which areperpendicular to an arrangement direction of the second LED cells. 10.The AC driven light emitting device of claim 6, wherein the third LEDcell has a top surface having a rough rectangular shape with two facinglonger sides and two facing shorter sides.
 11. The AC driven lightemitting device of claim 10, wherein the first and second electrodes ofthe third LED cell are respectively disposed adjacent to the two longersides of the top surface having the rectangular shape.
 12. The AC drivenlight emitting device of claim 10, wherein the third LED cell isarranged such that the longer side thereof is almost perpendicular to anarrangement direction of the third LED cells, and the first and secondelectrodes of the first LED cell are respectively disposed adjacent toboth sides on the top surface of the first LED cell, which are parallelto the arrangement direction of the first LED cells, and the first andsecond electrodes of the second LED cell are disposed adjacent to bothsides on the top surface of the second LED cell, which are parallel tothe arrangement direction of the second LED cells.
 13. The AC drivenlight emitting device of claim 12, wherein the first one of the firstLED cells extends along the third side of the top surface of thesubstrate to be adjacent to the first one of the second LED cells, andthe K^(th) second LED cell extends along the fourth side of the topsurface of the substrate to be adjacent to the K^(th) first LED cell.14. The AC driven light emitting device of claim 13, wherein the firstexternal electrode is placed on the first one of the first LED cells,and the second external electrode is placed on the K^(th) second LEDcell.
 15. The AC driven light emitting device of claim 13, wherein thefirst to third LED cells have almost the same light emission areas. 16.The AC driven light emitting device of claim 1, wherein the first tothird LED cells each comprise a first conductivity type semiconductorlayer, an active layer and a second conductivity type semiconductorlayer which are sequentially grown on the substrate.
 17. The AC drivenlight emitting device of claim 16, wherein at least one pair of the(2r−1)^(th) and 2r^(th) second LED cells is isolated from each other byan exposed region of the first conductivity type semiconductor layer,and shares one first electrode disposed in the exposed region of thefirst conductivity type semiconductor layer.
 18. The AC driven lightemitting device of claim 17, wherein at least one pair of the 2r^(th)and 2r+1^(th) first LED cells is isolated from each other by an exposedregion of the first conductivity type semiconductor layer, and sharesone first electrode disposed in the exposed region of the firstconductivity type semiconductor layer.
 19. The AC driven light emittingdevice of claim 18, wherein every pair of the (2r−1)^(th) and 2r^(th)second LED cells is isolated from each other by an exposed region of thefirst conductivity type semiconductor layer, and shares one firstelectrode disposed in the exposed region of the first conductivity typesemiconductor layer, every pair of the 2r^(th) and 2r+1^(th) first LEDcells is isolated from each other by an exposed region of the firstconductivity type semiconductor layer, and shares one first electrodedisposed in the exposed region of the first conductivity typesemiconductor layer, and other remaining first to third LED cells areisolated by exposed regions of the substrate.
 20. The AC driven lightemitting device of claim 1, wherein all the first to third LED cells areisolated from another adjacent LED cell by an exposed region of thesubstrate.